The present invention relates to apparatus for making holes in webs of paper or the like, and more particularly to improvements in apparatus for perforating webs of cigarette paper, tipping paper or other wrapping or confining materials which are utilized in the tobacco processing industry. Still more particularly, the invention relates to improvements in apparatus for making perforations in running webs of wrapping material or in the wrappers of discrete articles which constitute or form part of smokers' products and wherein the perforations are made by resorting to beams of coherent radiation.
It is already known to employ lasers or analogous sources of coherent radiation for the making of perforations in webs of cigarette paper, tipping paper or the like. It is also known to resort to lasers in connection with the making of holes directly in the wrappers of plain or filter cigarettes, filter rod sections and analogous rod-shaped articles which constitute or form part of smokers' products. Such apparatus normally further comprise means for transporting the material to be perforated into the range of coherent radiation as well as means for directing the radiation which issues from the source upon selected portions of the article or articles to be perforated. Lasers or analogous sources of coherent radiation can be used in connection with the making of holes in a wide variety of smokers' products, either prior to completion of such products (e.g., in the wrapping material which is to be applied to fillers and consists of webs of cigarette paper or tipping paper, sections of tipping paper or the like) or directly in the tubular wrappers of finished products (such as plain or filter tipped cigarettes, filter rod sections, plain or filter tipped cigarillos and others).
One of the primary reasons for perforating wrapping material, such as webs or sections of cigarette paper, tipping paper and the like, is that this provides the wrappers of finished products with zones of desired permeability which render it possible to control the nicotine and/or condensate contents of tobacco smoke. Apparatus for making such types of perforations are disclosed, for example, in U.S. Pat. No. 4,121,595 granted Oct. 24, 1978 to Uwe Heitmann et al., and in U.S. Pat. No. 4,281,670 granted Aug. 4, 1981 to Uwe Heitmann et al. An advantage of coherent radiation is that it can be used to provide a web of paper or the like with one or more zones of highly predictable permeability and also that the permeability is constant in each portion of such zone or zones, i.e., while the perforating apparatus is in uninterrupted use during an entire shift or much longer.
A modern filter tipping machine e.g., a machine known as MAX S which is produced and distributed by the assignee of the present application) normally produces pairs of filter cigarettes of unit length. As a rule, a continuous cigarette rod which is produced in a rod making machine (such as the machine known as PROTOS which is manufactured and sold by the assignee of the present application) is subdivided into a file of plain cigarettes of double unit length, and the direction of movement of successive plain cigarettes of double unit length is changed from axial to transverse so that the cigarettes form a row of parallel articles each of which is thereupon severed to yield two coaxial plain cigarettes of unit length. The cigarettes of each pair are moved axially of and away from each other to provide room for filter rod sections of double unit length. The thus obtained groups, each of which contains two plain cigarettes of unit length and a filter rod section of double unit length therebetween, are thereupon converted into filter cigarettes of double unit length by draping a uniting band of tipping paper around the filter rod section and around the adjacent inner end portions of the plain cigarettes of unit length. Each filter cigarette of double unit length is severed midway between its ends to yield two filter cigarettes of unit length.
In order to provide each cigarette of unit length with a so-called ventilation zone which admits atmospheric air into the column of tobacco smoke, it is customary to provide a web of tipping paper with one or more perforated zones prior to subdivision of the web into discrete uniting bands, or to make holes in the wrappers of finished filter cigarettes of unit length or double unit length. As a rule, each perforated zone consists of two or more rows of aligned perforations. To this end, and assuming that the perforations are made by beams of coherent radiation, the single beam which issues from a conventional laser is split once or more than once so as to provide a requisite number of split beams or partial beams, one for each row of perforations. A suitable mode of splitting a laser beam for such purposes is disclosed in the commonly owned U.S. patent application Ser. No. 294,815 filed Aug. 20, 1981 by Peter Pinck et al. The apparatus of Pinck et al. is quite satisfactory but rather expensive because repeated splitting of the laser beam necessitates a considerable outlay for the manufacture and adjustment of the optical systems which split the beam and focus the thus obtained split beams. Highly accurate splitting of the beam is not only desirable but in fact necessary because the permeability of the wrapper of each and every product (e.g., filter cigarette of unit length) of a long line of products should be maintained within an extremely narrow range.